The techniques of selective, localised laser melting and electron beam melting of powdered materials have previously been described in connection with the fabrication of three-dimensional bodies of amorphous metal, crystalline metal and nanocrystalline metal.
When cooling a metallic material from melt to solid phase, a polycrystalline structure is usually obtained. The microstructure consists of a large number of different grains where the atoms in each grain are arranged according to a regular pattern. If the atoms instead are completely disordered and there are no grains with regularly positioned atoms, the material is said to be amorphous. This can for example be achieved by cooling a melt very rapidly so that there is no time for any grains to grow.
U.S. Pat. No. 8,052,923 describes a technique in which a three dimensional body is built up layer-by-layer. A layer of metal powder is applied to a heat-conducting base, and a limited area of the layer is melted using a radiation gun such as a laser or an electron beam. The area is cooled so that the melted area solidifies into an amorphous metal. The melting process and cooling process can be successively repeated on new limited areas of the layer until a continuous layer of amorphous metal is formed. A new powder layer can then be applied and the melting and cooling processes repeated, the new layer being fused to underlying amorphous metal. With successive layers, a three dimensional body of amorphous metal can be formed.
Because small areas of the powder layers are melted at a time by the radiation gun, the melted areas can be cooled immediately. A small volume of melted alloy is easy to cool and the critical cooling speed for the melted volume to solidify into amorphous metal can be achieved.
U.S. Pat. No. 8,333,922 describes a further development to the technique described in U.S. Pat. No. 8,052,923. In U.S. Pat. No. 8,333,922 it is recognised that the melted areas can be cooled in accordance with a stipulated time-temperature curve in order to form a composite of crystalline or nanocrystalline metal particles in a matrix of amorphous metal. The method can be repeated until a continuous layer which contains composite metal to a desired extent is formed. Correspondingly, new powder layers can be applied and the method repeated for construction of a three-dimensional body having the requisite crystalline or nanocrystalline structure.
U.S. Pat. No. 8,333,922 also discloses that the two techniques can be combined, in which a limited area of already-formed amorphous metal is reheated by means of the radiation gun to a temperature above the glass transition temperature (Tg) of the material and the radiation gun is regulated in such a manner that the limited area is heat-treated in accordance with a stipulated time-temperature curve in order to transform the amorphous metal into a composite of crystalline or nanocrystalline metal particles in a matrix of amorphous metal. Suitable time-temperature curves can be established by means of TTT-diagrams (Time Temperature Transformation) and CCT-diagrams (Continuous Cooling Transformation).
The diagrams comprise a crystallization curve, a so-called nose, which shows the temperature and the time at which crystallization commences in the amorphous alloy in the supercooled state.
In the present invention, it has been recognised that these manufacturing techniques as described in U.S. Pat. No. 8,052,923 and U.S. Pat. No. 8,333,922 can be exploited and developed to impart specific and localised properties into the fabricated metal materials and to create new metal materials.
An object of the present invention is to provide a material having certain characteristics, e.g. magnetic anisotropy, which are localized at specific areas of the material.